Temporal, isotopic and spatial relations of early paleozoic gondwana-margin arc magmatism, Central Transantarctic Mountains, Antarctica

• Published in: Journal of Petrology
• Main Authors: Goodge, John W, Fanning, Christopher, Norman, Marc, Bennett, Victoria
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Oxford University Press
• Subjects: Keywords: deformation; fractionation; Gondwana; granite; granitoid; isotopic analysis; isotopic composition; magmatism; orogeny; Paleozoic; petrogenesis; spatial variation; subduction; temporal variation; uranium-lead dating; zircon; Antarctica Geochronology; Isotope geochemistry; Ross Orogen; Antarctic; East Antarctica; Transantarctic Mountains; Pacific; Nimrod; Nimrod Glacier; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/1885/67004; https://doi.org/10.1093/petrology/egs043; https://openresearch-repository.anu.edu.au/bitstream/1885/67004/5/Fanning_CM_RSES_2012_Temporal_isotopic.pdf.jpg; https://openresearch-repository.anu.edu.au/bitstream/1885/67004/7/01_Goodge_Temporal,_isotopic_and_spatial_2012.pdf.jpg

The Cambrian-Ordovician Ross Orogeny in Antarctica produced a voluminous magmatic belt composed mainly of post-orogenic granitoids. This magmatic belt has strong calc-alkaline characteristics reflecting a convergent-margin origin associated with subduction of paleo-Pacific oceanic lithosphere beneath cratonic East Antarctica. However, it is unclear how and when magmatism began, and to what degree magmatism was associated with syn-orogenic deformation and intra-arc extension. New U-Pb zircon ages, and whole-rock geochemical and Sr-Nd isotope data for granitoids sampled along a transect across the Ross Orogen in the Nimrod Glacier area of the central Transantarctic Mountains provide constraints on the timing, spatial variation, and origin of the magmatism in this area. This transect is one of the few places where the orogenic arc extends into the East Antarctic cratonic basement, thus helping to constrain both craton and arc evolution. New U-Pb ages show that magmatism was initiated as early as ∼590 Ma following latest Neoproterozoic rifting, that the magmatic belt is long-lived, lasting over about 100 Myr, and that the locus of magmatism shifted oceanward over time. Early syn-orogenic magmatism was focused within the leading edge of the cratonic basement, perhaps guided by strain partitioning during oblique subduction; younger magmas intruded a forearc sedimentary molasse basin, itself eroded from the earlier established arc system. Broadening of the arc during the later phases of Ross convergence indicates rollback of the subducting plate hinge and thickening of the developing forearc during continuing orogenic contraction. The granitoids mainly have calc-alkaline geochemical characteristics, but they show some similarity to adakitic compositions indicative of melt fractionation from the subducting slab; they do not show the alkaline signatures attributed in other areas to crustal extension. Inherited zircon components are compatible with melting of lower crust similar to that exposed at present in the Nimrod ...